Ramps 1.4 Pins to pins.h in Marlin Q

Could anyone explain to me the relationship between the placement of the pins on the ramps 1.4 board to the pins.h configurations. I am having a hard time understanding how to locate individual pins.

For example My Motherboard = 33. why is "#define FAN_PIN 9" what does the 9 stand for? is there a map that can be superimposed onto the ramps 1.4 blueprint to match Marlin assignments?

Apologies for Newb Questions

Janski

#if MOTHERBOARD == 33 || MOTHERBOARD == 35 || MOTHERBOARD == 67
    #define FAN_PIN            9 // (Sprinter config)
  #else
    #define FAN_PIN            4 // IO pin. Buffer needed
  #endif

  #if MOTHERBOARD == 77
    #define FAN_PIN            8 
  #endif
  
  #if MOTHERBOARD == 35
    #define CONTROLLERFAN_PIN  10 //Pin used for the fan to cool controller
  #endif

  #define PS_ON_PIN          12

  #if defined(REPRAP_DISCOUNT_SMART_CONTROLLER) || defined(G3D_PANEL)
    #define KILL_PIN           41
  #else
    #define KILL_PIN           -1
  #endif

  #if MOTHERBOARD == 35
    #define HEATER_0_PIN       8
  #else
    #define HEATER_0_PIN       10   // EXTRUDER 1
  #endif

  #if MOTHERBOARD == 33 || MOTHERBOARD == 67
    #define HEATER_1_PIN       -1
  #else
    #define HEATER_1_PIN       9    // EXTRUDER 2 (FAN On Sprinter)
  #endif

  #define HEATER_2_PIN       -1 

The 9 refers to the Arduino Mega pins..

If you trace the circuit, you'll find that D9 on the Arduino is the middle FET output. This is used as the FAN to blow on the extruder if you select board type 33.

Look at the schematic for the RAMPS 1.4 board (see the ramps wiki page), as the pins match the outputs from the Mega.

[www.reprap.org]

But what does the -1 stands for?
Is this some kind of placeholder for sth.?

Quote
derletztename
But what does the -1 stands for?
Is this some kind of placeholder for sth.?

Not defined.